Inkjet printing mechanisms use cartridges (often called "pens") which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For inatance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting," with the waste ink being collected in a "spittoon" reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solid content than the earlier dye based inks, which results in a higher optical density for the new inks. Unfortunately, the combination of small nozzles and pigmented ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, keeping the nozzle face plate clean becomes even more important when using pigment based inks, because they tend to accumulate more debris than the earlier dye based inks.
Two other earlier inkjet printing mechanisms using replaceable cartridges were the models 690C and 693C DeskJet.RTM. inkjet printers sold by the Hewlett-Packard Company of Palo Alto, Calif., the present assignee. This system used dye-based color inks and a pigment-based black ink, which had different servicing needs than the dye-based color inks. To maintain the desired ink drop size and trajectory, the area around the printhead nozzles must be kept reasonably clean. Wet ink and fibers of cotton, polyester, etc., often stick to the nozzle plate and the cheek areas adjacent the nozzle plate, particularly on a wide tri-color pen, causing print quality defects if not removed. This type of print quality defect is known as "fiber tracking," a problem which is more prevalent when printing with large volumes of black ink, which many consumers do when primarily printing text, indeed, many consumers use four or five black cartridges before replacing the full color cartridge.
Indeed, studies have shown that the type of fibers found inside a printer are typically made up of cotton and polyester fibers with a few animal hairs added, which are typically the same types of fibers that collect as dust balls in the corners of one's house. Wiping the nozzle plate only removes excess ink and other residue accumulated near the nozzle orifices, leaving the cheek regions unwiped to collect bits of dust, fabric fibers, animal hairs, and other debris.
Indeed, the DeskJet.RTM. 600 series of color inkjet printers produced by the Hewlett-Packard Company were particularly prone to fiber tracking print defects for several reasons. First, this series of printers uses the pigment-based black ink which was slow drying. Fibers that became attached to the print cartridges and the carriage hung down in the printzone to touch the paper, sometimes dragging into the black ink and creating fiber tracks. Fortunately, the dye based color inks did not have the same problem. Another reason this series of printers is prone to fiber tracking is that the wiper scraper cavities are located on the print cartridge, rather than in the service station. The wet ink and fibers that collect on the wiper are removed by contact with these wiper scraper cavities where the debris collects, according to design. This wiper scraper cavity design was favored because the inkjet cartridges used in these printers are disposable, so the collection of fiber debris was disposed of when the pen was replaced with a fresh cartridge. Moreover, in these printers the wiper does not wipe across the entire width of the pen, leaving portions of the front and back of the pen bottom which are not wiped and thus, free to collect fibers. Indeed, the 600 series of printers had carriage features which were at the same level as the pen, relative to the height of paper, and these surfaces came into direct contact with the wiper. Furthermore, the 600 series of inkjet printers requires more wiping to keep the pens healthy. More wiping means more wet ink which means the carriage becomes a welcome site for fiber collection soon after purchase, and fiber tracking service calls come in much sooner, as has been confined by monitoring calls to the manufacture's service center. Finally, after lengthy periods of inactivity, on the order of weeks or months, to begin in a print job the carriage first moves across the printzone to activate the media pick clutch, traveling over horizontal media support which has been collecting dust fibers during this period inactivity.
FIG. 7 shows how this fiber tracking problem occurred in a prior art inkjet printer. Here we see a color pen A and a black pen of B installed within an inkjet carriage C. The inkjet carriage C has pen alignment datums D which align the color pen B and the black A with respect to the printzone. The service station included a color wiper G and a black wiper H which respectively wiped a color printhead J of the color pen A, and a black printhead K of the black pen B. In this earlier wiping scheme, the wipers G and H removed fibers, debris and ink residue from the printheads J and K, but the wiper strokes stopped just past the edges of the printhead, leaving fibers F to collect on the four carriage datums D, as shown in a FIG. 7.
In one approach to addressing this fiber tracking problem, a translational wiping system using an orthogonal wiping stroke, was first sold by the Hewlett-Packard Company as the model 720C DeskJet.RTM. inkjet printer. To wipe the tri-color cartridge printhead, this system mounted a pair of auxiliary "cheek wipers" (also referred to by the designers as "mud flaps") to the wiper sled, adjacent a dual blade orifice plate wiper. There was no cheek wiping provided for the black printhead in this printer, which only used a dual-blade orifice plate wiper for the black pen. Thus, this system molded a total of six individual blades onto a stainless spring steel flame to form the wiper/mud flap assembly, two blades for the color orifice plate, two blades for the mud flaps, and two for the black orifice plate, all to service only two pens. The multitude of wiper blades made molding costly, not only in tooling costs, but all of these blades were difficult to remove as a unit from the mold, even using a one degree (1.degree.) draft on the blades. Difficulty in removing the blades from the molds lead to a high scrap rate, and thus, an increased cost for the parts that were successfully made, which in turn, increased the overall cost of the printer.